<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="text">
<input type="button" value="求和" onclick="f1()">
<input type="button" value="平方" onclick="f2()">
<div>结果：</div>
<script>
  let i = document.querySelector("input");
  let d = document.querySelector("div");
  function f1() {
    //d.innerText="结果:"+(i.value*1+i.value*1);
    d.innerText = "结果:"+(parseFloat(i.value)+parseFloat(i.value));
  }
  function f2() {
    if(isNaN(i.value)){
      d.innerText = "输入错误！";
      return;
    }
    d.innerText="结果:"+i.value*i.value;

    
  }
</script>

</body>
</html>